This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-188858, filed Jun. 23, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an impedance conversion circuit for use in an amplifier or the like constituted on an integrated circuit, and particularly to an improvement of frequency characteristics of an impedance conversion circuit.
2. Description of the Related Art
In recent years, the integration of semiconductors circuit built into an apparatus has been increasingly advanced. Above all, the signal processing portion, miniaturization and speed enhancement of an integrated circuit have been advanced and have resulted in digitization. However a circuit block in which analog processing is performed also exists on the grounds that it is difficult to develop digital processing. Examples of the circuit block in which analog signal processing is performed include a filter circuit which selects a desired signal in frequency domain.
The bandwidth of conventional active filters is of the order of several hundreds of kilohertz to several megahertz. On the other hand, the band required for broadband communication, hard disk lead channel, and the like is 100 times (about several hundreds of megahertz) the conventional band. Accordingly, the frequency characteristics of a transconductor (voltage-current converter) for use in the filter need to be strict. When the frequency characteristics of the transconductor for use in the filter deteriorate, the desired filter transmission characteristics cannot be realized, and normal reception cannot be performed. For example, to constitute a high-order filter, when the gain of an integrator using the transconductor becomes 1, and the phase deviates from xe2x88x9290 degrees, the frequency characteristics of the filter are influenced greatly.
While there are requests to broaden the band of the transconductor and amplifier constituting the filter, there are also requests for reducing current consumption.
A cascode connection has long been used in order to reduce a loss of the integrator and raise an output resistance of the transconductor, or to obtain the gain of the amplifier. The term, xe2x80x9ccascodexe2x80x9d, means a xe2x80x9ccascadexe2x80x9d connection in which a xe2x80x9ctriodexe2x80x9d (xe2x80x9ctrixe2x80x9d and xe2x80x9celectrodexe2x80x9d) is included.
As a technique by which a higher output impedance can be secured, there is an impedance conversion circuit called a regulated cascode circuit (hereinafter referred to as RGC circuit) using an operational amplifier and feedback technique shown in FIGS. 23 and 24 as introduced by K. BULT et. al., Analog Integrated Circuits and Signal Processing Vol. 1, No. 2, pp. 119 to 135, 1991, and the like. The entire contents of this reference being incorporated herein by reference.
FIG. 23 shows a bipolar transistor (Q0, Q1) as an amplification element, and FIG. 24 shows a field-effect transistor (M0, M1) as the amplification element. In the cascode connection, an amplification circuit (Q0 or M0) is connected in series on a collector or drain side of an emitter or source of the transistor (Q1 or M1), wherein an input-voltage Vin is connected to the base of the Q0 or the gate of the M0. An operational-amplifier A1 is connected to the base of the Q1 or the gate of the M1. The emitter or the source of the transistor (Q1 or M1) is connected to the inverting input terminal of A1, thereby realizing a negative feedback circuit for regulation.
A signal output is extracted from a node (Iout) on the collector or drain side of the transistor (Q1 or M1), and a very large output impedance can be realized. That is, the output resistance of the transconductor can be raised. When the cascode connection is used in the amplifier, a high gain can be realized. Note that an arrow in FIG. 23 shows a direction of a current flow.
It is, however, unable to disregard a parasitic capacity (Cp) between the base and the emitter of the transistor Q1 or the gate and the source of the M1, when the transistors are used in the RGC circuit at a high frequency of several hundreds of megahertz or more.
Accordingly, there arises a problem that it is unable to obtain satisfactory frequency characteristics at higher frequencies in an application of the above described RGC circuits including the impedance conversion circuit for transconductor circuits.
An object of the present invention is to provide an impedance conversion circuit in which satisfactory frequency characteristics can be maintained even at higher frequencies.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first current input terminal to which a first signal current is input, a first transistor having a base, collector, and emitter, the emitter being connected to the first current input terminal, a first amplifier circuitry connected between the emitter and the base of the first transistor, a second current input terminal to which a second signal current having a phase opposite to a phase of the first signal current is input, a second transistor having a base, collector, and emitter, the emitter being connected to the second current input terminal, a second amplifier circuitry connected between the emitter and the base of the second transistor, a first capacitive element connected between the base of the first transistor and the emitter of the second transistor, and a second capacitive element connected between the base of the second transistor and the emitter of the first transistor.
According to embodiments of the present invention, there is provided a transconductor circuit comprising, a first voltage input terminal to which a first signal voltage is input, a first current source connected to the first voltage input terminal, configured to generate a first signal current in proportion to the first signal voltage, a first transistor having a base, collector, and emitter, the emitter being connected to the first current source, a first amplifier circuitry connected between the emitter and the base of the first transistor, a second voltage input terminal to which a second signal voltage having a negative phase of the first signal voltage is input, a second current source connected to the second voltage input terminal, configured to generate a second signal current in proportion to the second signal voltage, a second transistor having a base, collector, and emitter, the emitter being connected to the second current source, a second amplifier circuitry connected between the emitter and the base of the second transistor, a first capacitive element connected between the base of the first transistor and the emitter of the second transistor, and a second capacitive element connected between the base of the second transistor and the emitter of the first transistor.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first current input terminal to which a first signal current is input, a first transistor having a gate, drain, and source, the source being connected to the first current input terminal, a first amplifier circuitry connected between the source and the gate of the first transistor, a second current input terminal to which a second signal current having a phase opposite to a phase of the first signal current is input, a second transistor having a gate, drain, and source, the source being connected to the second current input terminal, a second amplifier circuitry connected between the source and the gate of the second transistor, a first capacitive element connected between the gate of the first transistor and the source of the second transistor, and a second capacitive element connected between the gate of the second transistor and the source of the first transistor.
According to embodiments of the present invention, there is provided a transconductor circuit comprising, a first voltage input terminal to which a first signal voltage is input, a first current source connected to the first voltage input terminal, configured to generate a first signal current in proportion to the first signal voltage, a first transistor having a gate, drain, and source, the source being connected to the first current source, a first amplifier circuitry connected between the source and the gate of the first transistor, a second voltage input terminal to which a second signal voltage having a negative phase of the first signal voltage is input, a second current source connected to the second voltage input terminal, configured to generate a second signal current in proportion to the second signal voltage, a second transistor having a gate, drain, and source, the source being connected to the second current source, a first amplifier circuitry connected between the source and the gate of the second transistor, a first capacitive element connected between the gate of the first transistor and the source of the second transistor, and a second capacitive element connected between the gate of the second transistor and the source of the first transistor.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first current input terminal to which a first signal current is input, a first transistor having a base, collector, and emitter, the emitter being connected to the first current input terminal, a first amplifier circuitry connected between the emitter and the base of the first transistor, a second current input terminal to which a second signal current having a phase opposite to a phase of the first signal current is input, a second transistor having a base, collector, and emitter, the emitter being connected to the second current input terminal, a second amplifier circuitry connected between the emitter and the base of the second transistor, a third capacitive element connected between the base of the first transistor and the collector of the second transistor, and a fourth capacitive element connected between the base of the second transistor and the collector of the first transistor.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first current input terminal to which a first signal current is input, a first transistor having a gate, drain, and source, the source being connected to the first current input terminal, a first amplifier circuitry connected between the source and the gate of the first transistor, a second current input terminal to which a second signal current having a phase opposite to a phase of the first signal current is input, a second transistor having a gate, drain, and source, the source being connected to the second current input terminal, a second amplifier circuitry connected between the source and the gate of the second transistor, a third capacitive element connected between the gate of the first transistor and the drain of the second transistor, and a fourth capacitive element connected between the gate of the second transistor and the drain of the first transistor.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first current input terminal to which a first signal current is input, a first transistor having a base, collector, and emitter, the emitter being connected to the first current input terminal, a first amplifier circuitry connected between the emitter and the base of the first transistor, a second current input terminal to which a second signal current having a phase opposite to a phase of the first signal current is input, a second transistor having a base, collector, and emitter, the emitter being connected to the second current input terminal, a second amplifier circuitry connected between the emitter and the base of the second transistor, a first capacitive element connected between the base of the first transistor and the emitter of the second transistor, a second capacitive element connected between the base of the second transistor and the emitter of the first transistor, a third capacitive element connected between the base of the first transistor and the collector of the second transistor, and a fourth capacitive element connected between the base of the second transistor and the collector of the first transistor.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first current input terminal to which a first signal current is input, a first transistor having a gate, drain, and source, the source being connected to the first current input terminal, a first amplifier circuitry connected between the source and the gate of the first transistor, a second current input terminal to which a second signal current having a phase opposite to a phase of the first signal current is input, a second transistor having a gate, drain, and source, the source being connected to the second current input terminal, a second amplifier circuitry connected between the source and the gate of the second transistor, a first capacitive element connected between the gate of the first transistor and the source of the second transistor, a second capacitive element connected between the gate of the second transistor and the source of the first transistor, a third capacitive element connected between the gate of the first transistor and the drain of the second transistor, and a fourth capacitive element connected between the gate of the second transistor and the drain of the first transistor.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising a first active element, first inverting amplifier circuit whose input terminal is connected to an output end of the first active element, and whose output terminal is connected to a control end of the first active element, a second active element, a second inverting amplifier circuit whose input terminal is connected to an output end of the second active element, and whose output terminal is connected to a control end of the second active element, a first capacity element connected between the control end of the first active element and the output end of the second active element, and a second capacity element connected between the control end of the second active element and the output end of the first active element.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first active element, a first inverting amplifier circuit whose input terminal is connected to a first output end of the first active element, and whose output terminal is connected to a control end of the first active element, a second active element, a second inverting amplifier circuit whose input terminal is connected to a first output end of the second active element, and whose output terminal is connected to a control end of the second active element, a third capacity element connected between the control end of the first active element and a second output end of the second active element, and a fourth capacity element connected between the control end of the second active element and a second output end of the first active element.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first active element for controlling a current flowing between a first output end and a second output end in response to a signal applied to a control end, a first inverting amplifier circuit whose input terminal is connected to the first output end of the first active element, and whose output terminal is connected to the control end of the first active element, a second active element for controlling a current flowing between a first output end and a second output end in response to a signal applied to a control end, a second inverting amplifier circuit whose input terminal is connected to the first output end of the second active element, and whose output terminal is connected to the control end of the second active element, a first capacity element connected between the control end of the first active element and the first output end of the second active element, and a second capacity element connected between the control end of the second active element and the first output end of the first active element, wherein the second output end of the first active element is connected to a first current output terminal, the second output end of the second active element is connected to a second current output terminal, the first output end of the first active element is connected to a first current input terminal, the first output end of the second active element is connected to a second current input terminal, and polarities of the signals applied to the first current input terminal and the second current input terminal are reversed.
According to embodiments of the present invention, there is provided an impedance conversion circuit comprising, a first active element for controlling a current flowing between a first output end and a second output end in response to a signal applied to a control end, a first inverting amplifier circuit whose input terminal is connected to the first output end of the first active element, and whose output terminal is connected to the control end of the first active element, a second active element for controlling a current flowing between a first output end and a second output end in response to a signal applied to a control end, a second inverting amplifier circuit whose input terminal is connected to the first output end of the second active element, and whose output terminal is connected to the control end of the second active element, a third capacity element connected between the control end of the first active element and the second output end of the second active element, and a fourth capacity element connected between the control end of the second active element and the second output end of the first active element, wherein the second output end of the first active element is connected to a first current output terminal, the second output end of the second active element is connected to a second current output terminal, the first output end of the first active element is connected to a first current input terminal, the first output end of the second active element is connected to a second current input terminal, and polarities of the signals applied to the first current input terminal and the second current input terminal are reversed.